The present invention relates to a pallet supply apparatus for positioning a pallet such as a box (to be referred to as a "pallet" hereinafter) storing works such as assembling members or members to be processed in an automatic assembling system or an automatic processing system, and a control method thereof.
An automatic assembling apparatus or an automatic processing apparatus includes a pallet supply apparatus shown in prior art FIGS. 1A-4 for automatically conveying a pallet such as a box (to be referred to as a "pallet" hereinafter) storing works such as assembling members or members to be processed (to be referred to as "works" hereinafter) to a work supply position, and exchanging the pallet with a new pallet after all works in the pallet are picked up by a work supply robot of the automatic assembling system or the automatic processing system and the pallet becomes empty.
The pallet supply apparatus has a loaded pallet elevator 52a and an empty pallet elevator 52b, which are moved upward and downward by an equal distance in opposing direction via an endless chain 55, as shown in FIGS. 1A to 1F. The endless chain 55 is moved around a plurality of idler sprockets 57 in the clockwise direction indicated by an arrow CW or the counterclockwise direction indicated by an arrow CCW by a driving device including a motor 56a and a driving sprocket 56.
The loaded pallet elevator 52a is moved downward upon clockwise movement of the endless chain 55, and is moved upward upon counterclockwise movement of the endless chain 55. The empty pallet elevator 52b makes movements opposite to those of the elevator 52a. A pallet supply operation of this pallet supply apparatus is performed in the following cycle.
As shown in FIG. 1A, the loaded pallet elevator 52a is located at the lower end of its moving path, and the empty pallet elevator 52b is located at the upper end of its moving path. Pallets 130 to 133 each storing a predetermined number of works are inserted from the front surface of a main body 51 in the direction of an arrow Y, and are stacked on the loaded pallet elevator 52a. Then, the loaded pallet elevator 52a is moved upward so as to locate a left side flange (not shown) and a right side flange 130b of the uppermost pallet 130 above a shutter (not shown), which is arranged at the upper end of the main body 51, and stands by in an open state. After the shutter is closed, the elevator 52a is moved downward to separate the pallet 130 from the remaining pallets 131 to 133, as shown in FIG. 1B. In this manner, the pallet 130 separated on the shutter is positioned with reference to a predetermined reference surface by a positioning device (to be described later). As shown in FIG. 1C, every time a work is picked up by a work supply robot R of the automatic assembling system or the automatic processing system, the number of picked-up works is counted. When it is detected that all works in the pallet have been picked up, the empty pallet 130 is horizontally slid by the work supply robot R or a pusher (not shown), and is moved to a position above the empty pallet elevator 52b.
As shown in FIG. 1D, the empty pallet elevator 52b is moved upward to cause the left side flange and the right side flange 130b of the pallet 130 to float from the shutter, and the shutter is then opened to drop the pallet 130 onto the empty pallet elevator 52b. As shown in FIG. 1E, the loaded pallet elevator 52a is moved upward to locate a left side flange (not shown) and a right side flange 131b of the pallet 131 above the shutter in an open state. Then, as shown in FIG. 1F, the pallet 131 is separated from the remaining pallets 132 and 133, and is positioned at the work supply position. When the pallet 131 becomes empty, it is transferred onto the empty pallet elevator 52b, and the elevator 52b is moved downward. After the same steps are repeated for the pallets 132 and 133, the empty pallets stacked on the empty pallet elevator 52b are removed, and the empty pallet elevator 52b is moved to the lower end of its moving path. Thereafter, as shown in FIG. 1A, new pallets are inserted from the front surface of the main body 51. The above-mentioned cycle is automatically controlled by the following at least three different programs.
The pallet supply apparatus is automatically controlled on the basis of at least three different programs including an insertion mode program for inserting new pallets on the loaded pallet elevator 52a located at the lower end, as shown in FIG. 1A, after empty pallets are delivered from the main body 51, a separation mode program for separating the uppermost pallet on the loaded pallet elevator 52a from other pallets, as shown in FIG. 1B, and an automatic mode program for repeating the steps of recovering an empty pallet from which all works are picked up by the work supply robot onto the empty pallet elevator 52b by sliding the empty pallet to a position in front of the main body 51, and separating the uppermost one of the remaining pallets on the loaded pallet elevator 52a, as shown in FIGS. 1C to 1F. These programs are designed to prevent a decrease in automatic assembling or processing efficiency by minimizing the wait time of the work supply robot during an interval in which an empty pallet is exchanged with a pallet with works.
Conventionally, the pallet separated on the shutter is positioned by the positioning device shown in FIG. 2 or 3. The positioning device shown in FIG. 2 comprises an L-shaped arm 118 reciprocally moved by a cylinder 117, and rollers 119a and 119b supported by arms 118a and 118b of the L-shaped arm 118. A pallet 230 is moved by the rollers 119a and 119b toward a line N of intersection of two orthogonal reference surfaces 129 and 124.
The positioning device shown in FIG. 3 comprises rollers 128a, 128b, 129a, and 129b, each two of which are respectively supported by a pair of I-shaped arms 128 and 129. By driving cylinders 127a and 127b, the I-shaped arms 128 and 129 are moved toward orthogonal reference surfaces 229 and 224.
However, according to the above-mentioned prior art, when an empty pallet is slid along the shutter toward the empty pallet elevator, a long time is required for moving the positioning device backward. As a result, a time required for exchanging pallets is prolonged, and hence, an interrupt time of a work supply operation by the work supply robot is prolonged. More specifically, the positioning device shown in FIG. 2 requires a link device so as to prevent vibration of a pallet which is being positioned, and since the rollers contacting the two orthogonal side edges of the pallet are moved backward in the diagonal direction of the pallet, a long cylinder stroke is required until the two rollers are moved backward to positions where they do not interfere with the sliding pallet. For this reason, the time required for exchanging pallets is prolonged.
Also, the positioning device shown in FIG. 3 requires a large number of driving links since it must move at least one cylinder in the vertical direction together with the I-shaped arm and the two rollers supported by the arm. Therefore, the time required for driving these links is long.
Furthermore, automatic control as a combination of the above-mentioned insertion mode program, separation mode program, and automatic mode program starts the insertion mode program after all pallets become empty, and are recovered onto the empty pallet elevator 52b. During control of the insertion mode program, no pallet is present on the shutter, and the work supply robot must keep on waiting during this interval. In the automatic mode program, if a program is switched to the insertion mode program while the last pallet is positioned on the shutter, as indicated by a dotted line in FIG. 1A, and a work pick-up operation is being executed by the work supply robot, when the last pallet becomes empty, and is slid in the horizontal direction, it interferes with the empty pallet elevator located at the upper end, and the pallet or the empty pallet elevator may be damaged.
In addition to the above-mentioned problems, a pallet for supplying processing or assembling works normally has a cover so as to prevent dust or the like from becoming attached to these works. For this reason, when an assembling robot or the like picks up a work from the pallet, the cover must be detached from the pallet prior to the pick-up operation. FIG. 4 shows a conventional assembling system comprising a cover detaching device for detaching the cover.
In FIG. 4, a cover detaching device 200 comprises a chucking pad 204 for chucking a cover 202. The chucking pad 204 is attached to an arm 208, which is rotated about a rotational shaft 206, and is rotated by a rotary actuator 210. Therefore, the cover 202 chucked by the chucking pad 204 is detached from a pallet 212 upon operation of the rotary actuator 210, and in this state, the robot or the like is allowed to pick up works from the pallet 212. When all works are picked up from the pallet 212, the rotary actuator 210 is operated again to fit the cover 202 on the pallet 212. Thereafter, the empty pallet 212 is pushed by a robot finger 214 in the direction of an arrow A, and is slidably moved along the upper surface of a pallet stocker 216 from a robot accessible position to a delivery position.
However, in this prior art, during an interval from when the cover 202 is fitted on the pallet 212 until the empty pallet is delivered, the robot is occupied by the delivery operation of the empty pallet, and the operation efficiency of the entire assembling system is decreased. In order to solve this problem, the delivery operation of the empty pallet may be performed by an actuator other than the robot. However, when another actuator is added, cost of the entire assembling system is undesirably increased.